UNAIDS has set an ambitious target of 90-90-90 by 2020 to help end the AIDS epidemic wherein 90% of all HIV-infected people will know their status, 90% of those aware of their status will receive combination antiretroviral therapy (cART) and 90% of those on therapy will achieve virologic suppression. However, for this vision to be realized, 90-90-90 needs to be achieved in all populations especially those that are hardest to reach such as people who inject drugs (PWID) in low- and middle-income countries (LMICs). PWID in LMICs account for some of the fastest growing HIV epidemics that can be attributed to at least two factors: (1) inadequate access to HIV prevention services including HIV counseling and testing (HCT); and consequently, (2) low levels of linkage to care, initiation of ART and viral suppression. While viral suppression is the ultimate goal, there are several steps that lead to viral suppression - the first two steps and probably the most challenging steps are identifying infected PWID who are unaware of their status and linking them to care. There are several strategies focused on improving rates of retention in care and viral suppression being evaluated, but there are few trials underway to identify unaware and out-of-care individuals and link them to care particularly among PWID in LMICs. Beyond HIV, PWID also bear a disproportionately high burden of HCV infection with poor levels of knowledge and a care continuum far worse than what has been observed for HIV. Accordingly, this application is focused on developing and evaluating the cost-effectiveness of two strategies to identify PWID who are HIV-infected and not engaged in care in the community and link them to care centers. Strategy 1, time-based respondent-driven sampling (tRDS), focuses exclusively on network connections to identify infected individuals in the community, provide HIV/HCV testing and link infected persons to care centers. Strategy 2, respondent-driven sampling plus targeted field-based HIV testing (RDS+), utilizes a combination of network connections and spatially targeted field-based testing to identify infected individuals and link them to care. These two strategies will be evaluated using a cluster randomized trial approach across six Indian cities at varying stages of the HIV/PWID epidemic (e.g., historical vs. emerging) and differing geographic sizes (small cites vs. large cities). The primary endpoint of interest that will be compared across the two strategies will be the cost per HIV viremic (HIV RNA>1000 copies/ml) individual linked to care. Secondary outcomes include the cost per HIV-infected (previously unaware of status) individual identified and the cost per HCV-infected (previously unaware of status) individual identified. An additional objective of this application is to fine-tune these two strategies to maximize the cost-effectiveness of each approach. These interventions if cost-effective could be replicated in other high-, middle- and low-income settings to identify out-of-care HIV/HCV infected PWID in the community and link them to care.